Use of dual-pulse laser-induced breakdown spectroscopy with an orthogonal spark orientation is presented as a technique for trace metal analysis in bulk aqueous solutions. Two separate <i>Q</i>-switched Nd:YAG lasers operating at their fundamental wavelengths are used to form a subsurface, laser-induced plasma in a bulk aqueous solution that is spectroscopically analyzed for the <i>in situ</i> detection of Ca, Cr, and Zn. Optimizing the key experimental parameters of proper spark alignment, gate delay (<i>t</i><sub><i>d</i></sub>), gate width (<i>t</i><sub><i>b</i></sub>), and interpulse timing (Δ<i>T</i>) allowed experimentally determined detection limits of the order of micrograms per milliliter and submicrograms per milliliter. We present supporting evidence of a sampling mechanism that involves the formation of a cavitation bubble with the first pulse (<i>E</i><sub>1</sub>) followed by analysis of that bubble with a second pulse (<i>E</i><sub>2</sub>). The plasma created by <i>E</i><sub>2</sub> contains the analytically relevant information from the aqueous sample and often represents >250-fold enhancement over a single laser pulse with energy equal to <i>E</i><sub>1</sub> alone.
© 2003 Optical Society of America
William Pearman, Jon Scaffidi, and S. Michael Angel, "Dual-Pulse Laser-Induced Breakdown Spectroscopy in Bulk Aqueous Solution with an Orthogonal Beam Geometry," Appl. Opt. 42, 6085-6093 (2003)